Firedance is a novel written by Scott Baker. It was first published in 1985 and was the second Ashlu Cycle book.
Deadly Paths of Two-Soul Magic
Rafti is a beautiful firedancer - until she dies in a firepit and is brought back with a murdered girl's ghost-soul sharing her boy. Double-souled - the mark of the shaman - Rafti is forced to a new destiny by the priest who has resurrected her... Moth.
Moth, too, is double-souled, and cursed to discover the secrets of necromancy. He lives a life of nightmare paths, phantasmic visionquests and constant battle - he sails the River of Death, fights the World-Eel and the stars, steals from the palace of dead god and and from the thousand arms of the Earth goddess. And at every turn, Moth's teacher, his gods, his allies, his ancestors, and even his magical weapons try to kill him. And now Rafti joins him in a world where masters destroy their students and priests betray their gods. Because magic cannot be avoided.
But magic cannot be earned.
Only stolen. Stolen from the souls of the dead.